Process of producing ink sheet

ABSTRACT

PROCESS FOR PRODUCING INK SHEET TO BE EMPLOYED AS THE INK SOURCE IN A STENCIL PRINTING PROCESS COMPRISING FORMING AN ORGANIC SOLVENT SOLUTION OF A HIGH MOLECULAR WEIGHT COMPOUND AND A COLORLESS LEUCO DYE WHICH IS CAPABLE OF FORMING A COLORED DYE UPON CONTACT WITH AN ACIDIC MATERIAL AND APPLYING SAID SOLUTION TO A SUPPORT.

United States Patent 3,824,118 PROCESS OF PRODUCING INK SHEET MasayoshiTsuboi, Yasushi Yano, and Yoshiaki Suzuki, Asaka, Japan, assignors toFuji Photo Film Co., Ltd., Minami-ashigara, Kanagawa, Japan No Drawing.Continuation of abandoned application Ser. No. 840,501, July 9, 1969.This application Jan. 14, 1972, Ser. No. 218,008

Claims priority, application Japan, July 9, 1968,

Int. Cl. B41m 5/22 US. Cl. 117-362 2 Claims ABSTRACT OF THE DISCLOSUREProcess for producing ink sheet to be employed as the ink source in astencil printing process comprising forming an organic solvent solutionof a high molecular weight compound and a colorless leuco dye which iscapable of forming a colored dye upon contact with an acidic materialand applying said solution to a support.

This is a continuation of application Ser. No. 840,501, filed July 9',1969, now abandoned.

The present invention relates to a process of producing ink sheet. Moreparticularly, it relates to a process of producing ink sheet containingleuco dyes.

In the case of ordinary stencil printing methods such as mimeographing,a colored ink is applied to one side of a stencil having openingstherein while blank paper is supplied to the other side. The ink isforced through the openings of the stencil to form images on the blankpaper corresponding to the openings of the stencil. However, since theink is colored, it often stains not only the printing machine but theoperators body or clothes. More over, it is difficult to transporteither the ink or the printing machine with ease.

The inventors have discovered that stencil printing may be easilyconducted by employing an ink sheet containing colorless leuco dyes onor in a support in combination with paper coated with anelectron-accepting substance such as clay (hereinafter referred to asclaycoated paper), thereby remedying the above-mentioned defects. Thepresent invention relates to a process of producing such ink sheet.

It is accordingly an object of the present invention to provide aprocess of producing ink sheet which has superior printability.

Another object of this invention is to provide a process of producingink sheet capable of producing images excellent in durability.

These objects are attained by adding to a leuco dye solution a highmolecular weight compound having a melting point of from 45 C. to 210C., and applying the mixture thus obtained to a support, as by soaking asupport in the mixture.

As the leuco dyes to be employed in the products of the presentinvention, well-known chemical compounds which are normally colorless orlight-colored, but which form colored dyes when they come into contactwith solid acids can be used, such as benzoylleucomethylene blue,crystal violet lactone, malachite green lactone, Michlers hydrol,Michlers ketone, rhodamine B-lactame, acidrhodamine B-sultone, 3dimethylamino 7 methylaminobuorane, 3-dimethylamino-7 diarylfluorane.

The solvent used to dissolve the leuco dye is preferably a solvent whichis capable of dissolving more than 0.1% of the dye at room temperature,is free from offensive odor and has a boiling point of about 130 C. ormore. The boiling point of the solvent should not equal or be less thanthe melting pint or softening point of the synthetic high molecularcompound since the solvent would be vaporized, precipitating the leucodyes when the solvent was heated for the purpose of melting thesynthetic high molecular weight compound. Further, it often happensthat, if a highly polar solvent is employed, the leuco dye will be slowin coloring or will fail to form a colored dye at all, even when incontact with an electron-accepting compound. It is preferable,therefore, that non-polar solvents be employed. The solvents preferablyemployed in this invention are aromatic hydrocarbons such as toluene,xylene, trimethylbenzene, isopropylbenzene or ethylbenzene, chlorinatedhydrocarbons such as chlorobenzene, trichlorobenzene or chlorinateddiphenyl, or oxygen-containing solvents such as dibutyl ether, isobutylether, butyl acetate, amyl acetate, castor oil, or the like.

The synthetic high molecular weight compounds employed in this inventionare those which are not soluble in either the above leuco dye solventsor in a mixture of the above solvents with up to 8% of an auxiliarysolvent at a room temperature, but which are soluble to form ahomogeneous solution at a temperature higher than their melting pointsor softening range in such solvents and whose melting points orsoftening ranges vary from 45 C. to 210 C. If the melting point orsoftening range is lower than 45 C., it becomes soluble, and if themelting point or softening range is more than 210 C., it becomesnecessary to heat the synthetic high molecular weight compounds to sucha high temperature in order to dissolve them that decomposition of thedye may take place.

As synthetic high molecular Weight compounds to be employed in thepresent invention may be mentioned polyethylene, ethylene-vinyl acetatecopolymer, chlorinated polyethylene, polypropylene, vinyl chloride,polychorotrifluoroethylene, polytetrafluoroethylene,polyvinylpyrrolidone, ketone resins made from cyclohexanone andformalin, polybutadiene-1,2 (isotactic), polystyrene, synthetic rubber,polyamide resins made from dibasic aliphatic acids and polyamines andthe like.

Among the above, polyethylene, ethylene-vinyl acetate copolymer,polypropylene, polychlorotrifluoroethylene, polytetrafluoroethylene,ketone resins, synthetic rubber and polyamide resins are preferred.These synthetic high molecular weight compounds, even when heated, donot decompose to liberate acidic substances which cause the formation ofleuco dyes.

When the synthetic high molecular weight compounds are mixed with thesolution of solvent and leuco dyes, heated into a homogeneous solutionand then cooled, they will be disolved to such an extent that thesolution will not solidify. The most preferable synthetic high molecularweight compounds are those which, when they are dissolved in the leucodye solution, heated and cooled, the surface of the leuco dye layerfacing the air does not form a film, and moreover, in which the dye isseparated into fine particles having a diameter of p. or less, and inwhich the softening range or melting point of the mixture is under C.,whereby it is easily softened or melted. Such synthetic high molecularweight compounds comprise polyethylenes of low molecular weight (i.e.,having an average molecular weight of 600'- 8,000); polyethylene-vinylacetate resins having a vinyl acetate content of under 20% and a meltindex above 50; polytrifiuorochloroethylenes having a pour point above45 C. and an average molecular weight of LOGO-2,000; polyamide resinshaving amine value below 3; and ketone resins having an acid value below1.

The dye solutions of the present invention may be prepared by any of thefollowing methods:

(1) Dissolve the leuco dye in a solvent, add an auxiliary solvent ifnecessary, and mix the synthetic high molecular weight compound with themixture while heating.

(2) Heat the leuco dye, the synthetic high molecular compound and anorganic solvent into a homogeneous solution, adding subsidiary solventif necessary.

(3) Dissolve a leuco dye in a solvent, heat this solution to atemperature below the softening point or melting point of the synthetichigh molecular weight compound. Further add the synthetic high molecularWeight compound, which is melted by heating at a temperature above themelting point, while stirring vigorously. The system becomeshomogeneous, consisting of minutely dispersed particles of the synthetichigh molecular weight compound in the solution.

Of these methods, method (1) is the simplest and most preferred.

The leuco ink, prepared as above, is then applied to a support, undereither heating or cooling, to produce the ink sheet of this invention.

The preferred proportions of each component contained in 100 gr. of theink of this invention are set forth below.

The leuco dyes are present in the range of from 0.1 wt. percent to 20wt. percent of the ink composition. Amounts of 0.4 Wt. percent or aboveare preferred where the coloring ability of the particular leuco dye islow. Further, in general, it is preferred to employ amounts of leucodyes of about wt. percent or less.

The synthetic high molecular weight compound should be present in anamount of about 2 wt. percent or more, based upon the weight of leucoink, in order to plasticize the ink and increase its viscosity. However,it should not be present in an amount greater than about 28 wt. percentto obtain good printability. The synthetic high molecular weightcompound can be partially replaced with waxes, oils, fats, or finepowdered substances such as starch or powdered cellulose. The proportionof synthetic high molecular weight compound present has an importantbearing on the undesirable stickiness and the printability of the inksheet. For the purpose of producing ink sheet of good printability andreduced stickiness, it is particularly preferred that the proportion ofthe high molecular weight compound is between about 6 wt. percent andwt. percent.

The remainder of the ink composition comprises the leuco dye solventplus, if desired, an auxiliary solvent. Since, in many cases, the leucodye solvents dye badly after the commercially available stencil paperfor typewriting, it is preferred to employ as little of such solvents aspossible, so that flowing of the leuco dye solvents does not take place.As auxiliary solvents may be mentioned liquid paraffin, gasoline, soyabean oil, kerosene, silicone oil and the like. Especially, liquidparaffin is an excellent auxiliary solvent and is particularly preferredsince it decreases the temperature dependence of the viscosity of theink and is odorless. Liquid paraffin also enhances the stripping of theprotective sheet from the ink layer.

Two or more leuco dyes, solvents, and/or synthetic high molecular weightcompounds may be employed. Finely powdered substances solid at roomtemperature, paraflin, waxes, fats and oils, and/or a small quantity ofcoloring matter or pigment for improved appearance may also be added.

As the ink sheet support, a sheet-like substance which is relativelyunaffected by either the leuco dye solvents or the auxiliary solvents ispreferable. Further, a flexible sheet which is resistant to temperaturesof about 100 C. is preferable. Examples of such materials are aluminumfoil, non-woven fabrics, paper containing no acidic substances,cellophane sheet, polyethylene sheet, polyvinyl chloride sheet,polyester sheet, cellulose derivative sheet,poly(vinylchloridevinylidene) sheet, polypropylene sheet, polystyrenesheet, paperlike polystyrene sheet, or laminated sheet of theabove-mentioned polymer sheet and paper, laminated sheet of the aluminumfoil and paper, or cloth, or laminated sheet of cloth and paper. Also,polymer sheet or aluminum foil laminated with such porous layers aspaper, non-woven fabric, or thin, spongelike sheet may be used assupports.

The amount of leuco dye to be applied to the support varies according tothe number of copies to be made. For example, by means of an ink sheetcoated to a thickness of 0.1 mm. with an ink containing 2.0 g. of leucodyes in g. of the ink, more than 300 copies can be obtained.

The high molecular compounds contained in the ink sheet of thisinvention form, at room temperature, dispersed particles, uniformlyseparated from each other in the solution so that stickiness to thetouch is reduced. Moreover, by the use of this ink sheet, unevenness ofprinting is avoided since the leuco dye moves evenly to the paper to beprinted, due to the synthetic high molecular weight compounds which aredispersed uniformly on the sheet. In addition, the printed image isprotected by the synthetic high molecular weight compounds, which arepartly dissolved in the leuco dye solution at room temperature, thusincreasing the durability of the image. When materials such as waX,oils, fats or mineral oil were used, previously they sometimes formedlarge crystals over a period of time, and these coarse particles in theink layer would spoil the printability. In the case of the ink sheetcontaining synthetic high molecular weight compounds obtained by meansof this invention, however, fine particles of the synthetic highmolecular weight compounds are dispersed uniformly, no coarse particlesare being formed with the passage of time, and at the same time thestickiness of the ink sheet is remarkably decreased. Moreover, thesynthetic high molecular weight compounds condense foams between the inksheet and the stencil during the printing and remarkably improve theprintability by doing away with typographical broken ness or defacement.

EXAMPLE I 0.1 g. Crystalviolet lactone is dissolved in 6 g. ofchlorinated diphenyl. To this solution is added 1.0 g. of liquidparafiin, 2.0 g. of polyethylene having an average molecular weight of2,000 and a softening point of 107 C., and 1.0 g. of paratfin having amelting point of 62 C.- 64 C. The mixture is then heated at l20 C. toobtain a uniform, citrine and transparent solution. This solution isapplied to the cellophane side of cellophane laminated paper to athickness of g./m. Then a sheet of tissue paper is attached to it as aprotective sheet, thus producing the ink sheet. The tissue paper istaken off, a stencil is put on the ink layer, and copies are made onclay-coated paper with a handprinting mimeograph. During the printing,hands and clothes are not stained. The ink layer, cooled to roomtemperature, is colorless. It contains solid minute dispersed particlesof deposited polymer and paraflin. Stickiness is minimal.

EXAMPLE II 0.45 g. of Benzoylleucomethylene blue is dissolved in 8.55 g.of chlorinated diphenyl and the solution heated to 75 C. Then 1.2 g. ofpolytrifiuorochloroethylene (trade name: Daifloil 100, mobil temperature50-65 C., manufactured by Osaka Kinzoku Kogyo Kaisha Ltd.) is heated to75 C. The above-mentioned heated solution of benzoylleucomyethylene blueis then added to the heated polymer and the mixture stirred until auniform, transparent solution is obtained. This solution is cooled toroom temperature to produce an opaque paste. This paste is then coatedon the aluminum foil side of a laminated aluminum foil sheet and coveredwith a protective polypropylene film to produce the ink sheet. This inksheet is only slightly sticky, its color is citrine, and the protectivesheet can be easily peeled off. By printing in the same way as inExample I, clear blue prints are obtained.

EXAMPLE III 1.0 g. of rhodamine ,e-lactam is dissolved in 7.8 g. ofchlorinated diphenyl. To this solution is added 1.2 g. of

ketone resin (trade name: Hilac 110, manufactured by Hitachi Kasei KogyoKaisha Ltd.). Then this mixture is heated at 130 C. to obtain atransparent solution. After cooling to room temperature, this solutionis coated on polyester film to a thickness of 80 g./m. and covered withpolyvinylchloride film as the protective sheet to obtain the ink sheet.This ink sheet is easy to handle, and the proective sheet is easilypeeled off. The protective sheet taken off, the ink layer is placed uponthe stencil prepared by means of the electrostatic facsimile process(trade name: Stencil paper for Gestfax ES 390) and stencil printed onpaper coated with Japanese acid clay by means of multigraph. Thus aclear red printed paper is obtained. The printing is satisfactorilyconducted both at 5 C. and at 40 C. Almost no staining of hands andclothes occurs during the printing. 200 sheets of printed paper areobtainable.

EXAMPLE IV 1.0 g. of malachite green lactone is dissolved in 22 g. ofbutyl acetate. 15.0 g. of chlorinated triphenyl is then added graduallywhile heating. To this, 15.0 g. of liquid paraffin and 3.2 g. ofethylenevinyl acetate copolymer (trade name: Evaflex #420, manufacturedby Mitsui Polychemical Co. Ltd.) is added and the mixture heated at 100C. A nearly transparent solution is obtained. This hot solution iscoated on the cellophane side of cellophane laminated paper to obtain anink layer of 160 g./m. in thickness. Poly(vinyl-vinylidene cholride)film is put over it as a protective sheet and thus an ink sheet isobtained. Using this ink sheet and a stencil prepared by means of athermographic process (trade name: Risofax, manufactured by Riso KagakuKaisha Ltd.), a clear blue-green print is obtained by stenciling with anelectrorotary mimeograph on paper coated with attapulgite clay. This inksheet is colorless and only slightly sticky. At a speed of 80 sheets perminute and at a temperature of 9 C.35 C., over 450 sheets of prints areobtainable.

EXAMPLE V 2.0 g. of crystalviolet lactone and 2.4 g. of leucomethyleneblue are dissolved in a mixed solvent of 70.6 g. of chlorinated diphenyland 13.0 g. of kerosene, 14.5 g. of polyamide resin (trade name: Hitamid502, manufactured by Hitachi Kasei Kogyo Kaisha Ltd.) is added to it.The mixture is then heated to 120 C. to obtain a clear solution. Afterbeing cooled to about 40 C., this solution is applied to a polyesterfilm in the thickness of 60 g./m. Glassine paper is put over it as aprotective sheet, and the ink sheet is obtained. This ink sheet, lightcreamy in color, is only slightly sticky, and the proective sheet iseasily peeled off. The protective sheet taken off, the ink sheet isafiixed to the frame of a mimeograph together with a wax stencil. Byprinting with a clean roller, clear, blue prints are obtained. Printingis successful at both 5 C. and 40 C.

EXAMPLE VI 1.0 g. of 3-diethylamino-7-methylaminofiuoran is dissolved in20.0 g. of chlorinated diphenyl. To this solution is added 50.0 g. ofliquid parafiin, 13.0 g. of polyethylene of average molecular weight5,000, and the mixture heated to 120 C. to obtain a clear solution. Thenthis solution is cooled to about 60 C., applied in a thickness of about100 g./m. to the non-woven fabric side of a cellophane sheet laminatedwith non-Woven cellulose fabric. Aluminum foil is put over it as aprotective sheet, and thus the ink sheet is produced. The protectivesheet is taken off, White Mirya stencil (manufactured by Horii ToshadoKaisha Ltd.) put over the ink sheet, and printing performed on papercoated with bentonite and magnesium oxide to produce black prints. Morethan 300 prints are obtainable with this ink sheet. The ink sheet iscolorless and no staining of hands or clothes is experienced. Handlingis easy because the ink sheet is semi-dry.

With regard to the above examples, Daifloil is apolytrifluorochloroethylene having a degree of polymerization of 1,300and a softening range of 50 to 65 C.; Hilac 110 is a copolymer preparedfrom cyclohexanone and formaldehyde and having a softening range of 110to 130 C.; Evafiex 420 is an ethylene-vinyl acetate copolymer containing18% vinyl acetate and having a softening point of 99 C.; and Hitamid 502is a copolymer prepared from an aliphatic acid and a polyamine andhaving a softening range of to C.

What we claim is:

1. A process for producing an ink sheet useful in a stenciling process,said sheet comprising a support carrying a solution of a colorless inkcoated thereon, said solution being of a viscosity suitable for use asan ink in a stenciling process, which comprises the steps of (a)dissolving in a non-polar organic solvent selected from the groupconsisting essentially of aromatic hydrocarbons, aromatic chlorinatedhydrocarbons and oxygen-containing solvents, a substantially colorlessleuco ink, in an amount of from about 0.1 to about 20.0%, by weight, ofthe ink composition, said ink capable of forming a colored ink whencoming in contact with an electron-accepting solid acidic material,

(b) mixing with the solution thus formed, an organic synthetic highmolecular weight compound selected from the group consisting ofchlorinated polyethylene, vinyl chloride, polyvinyl pyrrolidone,isotactic polybutadiene-1,2 and polystyrene, having a melting orsoftening point ranging from about 45 C. to about 210 C., said compoundbeing present in an amount ranging from about 2.0% to about 28.0% byweight, of the leuco ink, and said compound being insoluble in saidsolvent at room temperature,

(c) heating the mixture thus formed to a temperature higher than themelting or softening point of the organic synthetic high molecularweight compound, thereby forming a homogeneous solution,

(d) cooling the solution thus formed to a temperature lower than themelting or softening point of said organic synthetic high molecularweight compound, thereby forming a dispersion of said organic synthetichigh molecular weight compound, and

(e) applying the resulting dispersion to a suitable sup port,

said resulting solution maintained on said support in a non-solidifiedstate of a viscosity suitable for use as an ink in a stenciling process,and

said high molecular weight compound and said dye capable of beingtransferred when said ink sheet is contacted with a receptive sheet.

2. A process for producing an ink sheet useful in a stenciling process,said sheet comprising a support carrying a solution of a colorless inkcoated thereon, said solution being of a viscosity suitable for use asan ink in a stenciling process, which comprises the steps of:

(a) dissolving in a non-polar organic solvent selected from the groupconsisting essentially of aromatic hydrocarbons, aromatic chlorinatedhydrocarbons and oxygen-containing solvents, a substantially colorlessleuco ink, in an amount of from about 0.1 to about 20.0% by weight, ofthe ink composition, said ink capable of forming a colored ink whencoming in con tact with an electron-accepting solid acidic material,

(b) mixing the solution thus formed, an organic synthetic high molecularweight, compound selected from the group consisting of polyethylene,ethylenevinyl acetate copolymer, polypropylene,polychlorotrifiuoroethylene, polytetrafiuoroethylene, ketone resins,synthetic rubber, and polyamide resins,

(c) heating the mixture thus formed to a temperature higher than themelting or softening point of the organic synthetic high molecularweight compound, thereby forming a homogeneous solution,

((1) cooling the solution thus formed to a temperature lower than themelting or softening point of said organic synthetic high molecularweight compound, thereby forming a dispersion of said oragnic synthetichigh molecular weight compound, and (e) applying the resultingdispersion to a suitable supsaid resulting solution maintained on saidsupport in a non-solidified state of a viscosity suitable for use as anink in a stenciling process, and said high molecular weight compound andsaid References Cited UNITED STATES PATENTS 3,079,351 2/1963 Staneslowet a1. 11736.2 3,418,148 12/1968 Barz 117-36.1

MURRAY KATZ, Primary Examiner US. Cl. X.R.

dye capable of being transferred when said ink 10 1l7l38.8 UA, 155 UA,132 C sheet is contacted with a receptive sheet.

UNITED STATES PATENT OFFICE CERTIFICATE OF QQRRECTION Patent No. 824:,118 Dat d July 16, 1974 Invent0r(s) Masayoshi TSUBOI et a1 It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

IN THE CLAIMS:

Column 6, claim 2, line 64 following "mixing" insert with Signed endsealed this 11th day of March 1.975.

(SEAL) Attest:

a C. MARSHALL DANN RUTH C r-IASON Commissioner of Patents. AttestlngOfficer and Trademarks

